Abstract

Ice sheet flow is strongly influenced by the nature and quantity of meltwater entering the subglacial
system. Accessing and monitoring contemporary drainage systems beneath ice sheets is notoriously
difficult, but it is possible to utilise the exposed beds of palaeo-ice sheets. In particular, eskers record
deposition in glacial drainage channels and are widespread on the exposed beds of former ice sheets.
However, unlike some other common glacial landforms (e.g. drumlins) there have been relatively few
attempts to investigate and quantify their characteristics at the ice sheet scale. This paper presents data
on the distribution, pattern, and morphometry of a large (>20,000) sample of eskers in Canada, formed
under the Laurentide Ice Sheet, including quantification of their length, fragmentation, sinuosity, lateral
spacing, number of tributaries, and downstream elevation changes. Results indicate that eskers are
typically very long (hundreds of km) and often very straight (mean sinuosity approximates 1). We
interpret these long esker systems to reflect time-transgressive formation in long, stable conduits
under hydrostatic pressure. The longest eskers (in the Keewatin sector) are also the least fragmented,
which we interpret to reflect formation at an ice margin experiencing stable and gradual retreat. In many
locations, the lateral distance between neighbouring eskers is remarkably consistent and results
indicate a preferred spacing of around 12 km, consistent with numerical models which predict esker
spacing of 8e25 km. In other locations, typically over soft sediments, eskers are rarer and their patterns
are more chaotic, reflecting fewer large R-channels and rapidly changing ice sheet dynamics. Comparison
of esker patterns with an existing ice margin chronology reveals that the meltwater drainage system
evolved during deglaciation: eskers became more closely spaced with fewer tributaries as deglaciation
progressed, which has been interpreted to reflect increased meltwater supply from surface melt. Eskers
show no preference to trend up or down slopes, indicating that ice surface was an important control on
their location and that the conduits were, in places, close to ice overburden pressure.

Item Type:

Article

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